The earliest road traffic barriers for use at worksites were made from concrete and have a broad base which tapered to an apex such as disclosed in U.S. Pat. No. 4,059,362. Although they provide an effective barrier and are still widely used, the impact of a vehicle with them usually causes severe damage to both the vehicle and its occupants.
Accordingly concrete barriers have been progressively replaced at worksites by hollow modules made from semi rigid plastic material, usually polyethylene, which are filled with water to increase their weight and to provide an effective barrier, such as disclosed in AU Patent 664774. The aim is for the barrier to deform and move moderately when impacted by a vehicle thus absorbing the impact energy and minimizing damage to the vehicle and its occupants.
However the latter molded barrier is much the same shape as the earlier concrete barriers and vehicles tend to climb up them and roll over which still causes considerable damage. An early attempt to both strengthen a coupled chain of water filled barriers and to also soften the impact of a vehicle with the barrier is taught in U.S. Pat. No. 5,531,540. Here a pair of continuous tubular crash rails is mounted on the side walls of water filled modules by means of metal brackets strapped to the modules.
Although the mounting brackets of this configuration have been variously modified in later versions, it still does not achieve the optimum trade off between providing a barrier which limits the travel of an impacting vehicle and at the same time minimizes damage to the vehicle and its occupants. A further attempt to achieve this trade off is disclosed in AU Patent 751778 where the cross section of the water filled module is changed from an A shape to a castellation shape with an enlarged top section to prevent the vehicle wheel from climbing the barrier. The modules are also firmly bolted together to provide a continuous barrier which resists fracture.
AU Patent 774224 takes a step back toward the rigidity of the original concrete barriers by tying water filled modules together with a metal beam which is mounted on and overlies the side walls of at least two adjoining modules. The resulting barrier tends to have the rigidity of a concrete barrier and very little impact energy is absorbed by the barrier. Accordingly the vehicle and its occupants absorb most of the impact energy which usually causes severe damage.
In our PCT Application WO2004009909 we also teach the use of a metal beam but in a quite different way from AU774224 in that the beam is mounted on individual modules by means of a deformable bracket. Accordingly the beam and brackets absorb the initial impact energy and because they do not tie the modules together, the chain of coupled modules is still flexible enough to absorb further kinetic energy by flexing within the standard limits of displacement for road barriers. We have found that this arrangement meets the requirements of Australian New Zealand Road barrier Standard 3845-1999 and US NCHRP 350 for road safety barrier systems. Road safety barrier systems are now required to meet crash test standards set by road regulatory State and Federal agencies.
Another attempt to combine flexibility with limited displacement in barriers having water filled modules of castellated cross sectional shape has been made by fitting an internal steel frame, tying the modules together using cables running over the top of the modules. The cables are clamped to fixtures on each module thus forming a continuous linked barrier. However clamping the cables on top of the modules is time consuming and lack of tension in the cables is not ideal for the integrity of the linked barrier. Further the system suffers from uncontrolled deflection and cannot be used where traffic buffer space is restricted.